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F Artaud

Publications and source records attributed to F Artaud.

At least 19 recordsLinked to original sources
PubMed1999

Contribution of endogenously formed arachidonic acid in the presynaptic facilitatory effects of NMDA and carbachol on dopamine release in the mouse striatum.

Arachidonic acid stimulated the release of [3H]-dopamine from striatal microdiscs in a concentration-dependent and partially calcium-dependent manner. Inhibitors of cytosolic and membrane-bound phospholipase A2 were used to determine whether endogenously formed arachidonic acid also contributes to the release of [3H]-DA (previously taken up in tissues or endogenously synthesized from [3H]-tyrosine) evoked by N-methyl-d-aspartate (NMDA) and carbachol alone or in combination. In the presence of magnesium, carbachol was found to remove the magnesium block of NMDA receptors and to facilitate the NMDA-evoked release of [3H]-DA from striatal microdiscs and synaptosomes. In addition, in the absence of magnesium, synergistic responses were induced by both agonists on microdiscs but not on synaptosomes. Responses induced by NMDA, carbachol or both agonists on microdiscs were reduced by phospholipase A2 inhibitors, the most striking effects being observed with mepacrine. Mepacrine was also shown to reduce the oxotremorine, but neither the nicotine- nor the potassium-evoked release of [3H]-DA. Tetrodotoxin decreased the release of [3H]-DA evoked by the co-application of NMDA and carbachol on microdiscs, but mepacrine still decreased this tetrodotoxin-resistant response. Similarly, mepacrine still decreased the release of [3H]-DA evoked by NMDA and carbachol on synaptosomes. Altogether, these results indicate that arachidonic acid which is formed in striatal neurons, and to a lesser extent in DA fibres, under stimulation of NMDA and muscarinic receptors, partially contributes to the presynaptic facilitation of DA release evoked by NMDA and carbachol.

Animals↗
PubMed1998

Lack of autoreceptor-mediated inhibitory control of dopamine release in striatal synaptosomes of D2 receptor-deficient mice.

Mouse purified striatal synaptosomes were used to study the release of newly synthesised [3H]-dopamine ([3H]-DA) or of previously taken up [3H]-DA. Quinpirole (QP, 10 microM), a D2/D3 dopaminergic agonist, was found to reduce the release of newly synthesised [3H]-DA with a larger amplitude when 4-aminopyridine (100 microM) instead than veratridine (1 microM) or potassium (25 mM) was used to evoke DA release. Among the different D2/D3 dopaminergic agonists tested R(-)-propylnorapomorphine (NPA) and quinpirole were the most potent. These compounds reduced, in a concentration-dependent manner, the 4-aminopyridine-evoked release of [3H]-DA previously taken up by synaptosomes (50% maximal inhibition). In contrast, the D3 agonist PD-128,907 had little effect even when used at 100 nM. The QP (100 nM)-induced response was completely antagonised by sulpiride (1 microM). Strikingly, the NPA (100 nM) and PD-128,907 (100 nM)-evoked responses were completely suppressed in D2 receptor-deficient mice. This data strongly suggest that only D2 but not D3 receptors are involved in the autoreceptor-mediated inhibition of the evoked release of [3H]-DA. Interestingly, while amphetamine-induced release of [3H]-DA was not modified, a slight reduction of [3H]-DA efflux induced by the dopamine (DA) uptake inhibitor cocaine was observed in D2 receptor-deficient mice.

4-Aminopyridine↗
PubMed1998

Direct and indirect presynaptic control of dopamine release by excitatory amino acids.

Dopamine (DA) release from nerve terminals of the nigrostriatal DA neurons not only depends on the activity of nigral DA cells but also on presynaptic regulation. Glutamatergic neurons of cortical origin play a prominent role in these presynaptic regulations. The direct glutamatergic presynaptic control of DA release is mediated by N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA) receptors, located on DA nerve terminals. In addition, by acting on striatal target cells, these glutamatergic neurons contribute also to indirect regulations of DA release involving several transmitters such as GABA, acetylcholine and neuropeptides. Diffusible messengers such as nitric oxide (NO) or arachidonic acid (AA) which are particularly formed under the stimulation of NMDA receptors may also participate to the regulation of DA release. In the present study, it will be shown that the co-application of NMDA and carbachol synergistically increases the release of [3H]-DA and that this effect is reduced by mepacrine or 4-bromophenacylbromide (10(-7) M), two inhibitors of PLA2. Therefore endogenously released AA induced by the co-stimulation of NMDA and cholinergic receptors seems to be involved, at least partly, in the release of DA.

Animals↗
PubMed1996

Stimulatory effect of arachidonic acid on the release of GABA in matrix-enriched areas from the rat striatum.

Arachidonic acid was shown to stimulate the release of preloaded [3H]GABA from microdiscs of tissue punched out in matrix-enriched areas of the rat striatum. This effect, which was calcium- and dose-dependent, persisted in the presence of inhibitors of arachidonic acid catabolism. Other fatty acids were less or not effective. Arachidonic acid also inhibited [3H]GABA uptake into purified striatal synaptosomes, however the arachidonic acid-evoked release of [3H]GABA persisted following inhibition of the GABA neuronal uptake process. The stimulatory effect of arachidonic acid on GABA release may largely result from the activation of a protein kinase C since the arachidonic acid response was reduced by several protein kinase C inhibitors. Arachidonic acid also dose-dependently stimulated the release of preloaded [3H]GABA from purified striatal synaptosomes. Similar results were obtained when synaptosomes were previously incubated with [3H]glutamine to study the release of endogenously synthesized [3H]GABA. Further indicating a direct action of the fatty acid on GABAergic neurons, the arachidonic acid-induced release of [3H]GABA from microdiscs was not modified in the presence of the D1 dopaminergic antagonist SCH23390 or of glutamatergic antagonists. Finally, the release of [3H]GABA evoked by the combined application of NMDA and carbachol (a treatment known to markedly stimulate arachidonic acid formation) was reduced by inhibitors of phospholipase A2 further indicating that endogenously formed arachidonic acid significantly facilitates the release of GABA in the striatum.

Animals↗
PubMed1994

NMDA and carbachol but not AMPA affect differently the release of [3H]GABA in striosome- and matrix-enriched areas of the rat striatum.

The effects of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA; 10(-3) M), N-methyl-D-aspartate (10(-3) M, in the absence of magnesium or presence of AMPA) and carbachol (10(-3) M) on the release of preloaded [3H]gamma-aminobutyric acid ([3H]GABA) from microdiscs of tissue punched out from sagittal brain slices in striosome- or matrix-enriched areas of the rat striatum have been compared. Although AMPA stimulated similarly the release of [3H]GABA in both striatal compartments, the release of [3H]GABA evoked by either N-methyl-D-aspartate (in the presence of AMPA) or carbachol was more pronounced in matrix- than in striosome-enriched areas. AMPA- and N-methyl-D-aspartate- (in the absence of magnesium) evoked responses were reduced but not abolished in the presence of tetrodotoxin (10(-6) M) in both compartments while the carbachol-evoked release of [3H]GABA was decreased by tetrodotoxin only in the matrix. The interruption of cholinergic transmission by the combined application of atropine (10(-5) M) and pempidine (10(-4) M) was without effect on the AMPA-evoked release of [3H]GABA, but it reduced the N-methyl-D-aspartate- (in the absence of magnesium or presence of AMPA) evoked release of [3H]GABA in both compartments, these reductions being of similar amplitude than those observed with tetrodotoxin.

Animals↗
PubMed1992

Modulation of GABA release by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and N-methyl-D-aspartate receptors in matrix-enriched areas of the rat striatum.

Using a new in vitro superfusion device, the release of preloaded [3H]GABA was examined in microdiscs of tissues taken from sagittal slices in matrix-enriched areas of the rat striatum. Potassium (9 mM, 15 mM) stimulated the release of [3H]GABA in a concentration- and calcium-dependent manner and the veratridine (1 microM)-evoked release of [3H]GABA was completely abolished in the presence of tetrodotoxin (1 microM). The selective glutamatergic agonist alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM) enhanced the potassium-evoked release of [3H]GABA as well as the basal outflow of [3H]GABA. This latter effect was found to be calcium-dependent, partially diminished by tetrodotoxin (1 microM), completely blocked by 6,7-dinitro-quinoxaline-2,3-dione (0.1 mM), which is generally used as an antagonist of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors, but not affected by (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK801, 10 microM), a specific antagonist of N-methyl-D-aspartate receptors. Similarly, N-methyl-D-aspartate (1 mM) enhanced both the potassium (9 mM) and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM)-evoked release of [3H]GABA but when used alone, due to the presence of magnesium in the superfusion medium, was ineffective on the basal efflux of [3H]GABA. A stimulatory effect of N-methyl-D-aspartate (1 mM) on the basal outflow of [3H]GABA was observed, however, when magnesium was omitted from the superfusion medium. The stimulatory effect of N-methyl-D-aspartate (1 mM) observed in the presence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate was not potentiated by glycine (1 microM, in the presence of strychnine 1 microM) and the N-methyl-D-aspartate-evoked response seen in the absence of magnesium was not enhanced by D-serine (1 mM), suggesting that endogenous glycine is already acting on N-methyl-D-aspartate receptors. In fact, in the absence of magnesium, 7-chloro-kynurenate (1 mM) completely abolished the stimulatory effect of N-methyl-D-aspartate on the release of [3H]GABA confirming that under our conditions, the glycine site of the N-methyl-D-aspartate receptor is saturated. N-methyl-D-aspartate-evoked responses were all blocked by MK801 (10 microM). Finally, the N-methyl-D-aspartate-evoked response seen in the absence of magnesium was markedly reduced in the presence of tetrodotoxin (1 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

L-glutamate-evoked release of dopamine from synaptosomes of the rat striatum: involvement of AMPA and N-methyl-D-aspartate receptors.

Previously, using purified synaptosomes from the rat striatum, we have shown that agonists of D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors stimulate the release of [3H]dopamine continuously synthesized from [3H]tyrosine. Similar results were obtained with N-methyl-D-aspartate in the absence of magnesium. In the present study, using the same approach, attempts were made to determine whether in the presence of magnesium, the combined stimulation of AMPA receptors allows us to demonstrate the presynaptic facilitation of [3H]dopamine release through N-methyl-D-aspartate receptors. L-Glutamate (10(-3) M) markedly stimulated the release of [3H]dopamine from synaptosomes, this effect being about twice that found with AMPA (10(-3) M) while N-methyl-D-aspartate (10(-3) M) even in the presence of glycine (10(-6) M) was ineffective. In agreement with previous results, a stimulatory effect of N-methyl-D-aspartate and glycine was only observed in the absence of magnesium. This response was blocked by 6,7-dinitro-quinoxaline-2,3-dione (3 x 10(-5) M), confirming that this compound, generally used as an AMPA antagonist, also blocks N-methyl-D-aspartate receptors. The AMPA (10(-3) M)-evoked release of [3H]dopamine was markedly potentiated by the combined application of N-methyl-D-aspartate (10(-3) M) and glycine (10(-6) M) in the presence of strychnine, indicating that the concomitant activation of AMPA receptors removes the voltage-dependent magnesium block of N-methyl-D-aspartate receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Specific role of N-acetyl-aspartyl-glutamate in the in vivo regulation of dopamine release from dendrites and nerve terminals of nigrostriatal dopaminergic neurons in the cat.

Levels of N-acetyl-aspartyl-glutamate measured by high-pressure liquid chromatography were found to be very high in the cat substantia nigra, particularly in the pars compacta, while those in the caudate nucleus were much lower. In halothane-anaesthetized cats implanted with push-pull cannulae, N-acetyl-aspartyl-glutamate (10(-8) M) induced a marked and prolonged release of newly synthesized [3H]dopamine, when infused into the posterior but not into the anterior part of the caudate nucleus. In contrast, in the presence of tetrodotoxin (10(-6) M), N-acetyl-aspartyl-glutamate (10(-8) M) reduced the residual release of [3H]dopamine; this effect was also more pronounced in the posterior than in the anterior part. In the conditions used, as indicated by experiments with [3H]N-acetyl-aspartyl-glutamate no glutamate was formed from the infused N-acetyl-aspartyl-glutamate. Ibotenate (10(-5) M) induced changes in [3H]dopamine release in both the absence and presence of tetrodotoxin, which were closely similar to those observed with N-acetyl-aspartyl-glutamate. Responses induced by either N-acetyl-aspartyl-glutamate or ibotenate were not mediated by N-methyl-D-aspartate receptors since N-methyl-D-aspartate stimulated the release of [3H]dopamine only when used in a high concentration (10(-4) M) and applied in a magnesium-free superfusion medium in both the presence of glycine (10(-6) M) and strychnine (10(-6) M). In addition, the stimulatory effect of N-methyl-D-aspartate persisted in the presence of tetrodotoxin; it was of similar amplitude in both parts of the caudate nucleus and of shorter duration than that evoked by either N-acetyl-aspartyl-glutamate or ibotenate alone. N-Acetyl-aspartyl-glutamate interacted with dopaminergic neurons not only presynaptically in the caudate nucleus but also in the substantia nigra since a marked increase in [3H]dopamine release was observed both from local dendrites and from nerve terminals in the ipsilateral caudate nucleus when N-acetyl-aspartyl-glutamate (10(-7) M) was infused locally into the substantia nigra pars compacta. No effect could be seen in contralateral structures. The isomer of natural N-acetyl-aspartyl-glutamate, beta-N-acetyl-aspartyl-glutamate (10(-7) M), had no effect on [3H]dopamine release when applied similarly in the substantia nigra, thus confirming the specificity of the action of N-acetyl-aspartyl-glutamate.

Animals↗
PubMed1991

Presynaptic facilitation of dopamine release through D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors on synaptosomes from the rat striatum.

Purified synaptosomes from the rat striatum were superfused continuously with [3H]tyrosine in order to estimate the release of newly synthesized [3H]dopamine. When tested from 10(-6) to 10(-3) M, several excitatory amino acids or their analogues markedly stimulated the release of [3H]dopamine, their apparent rank order of potency being kainate greater than glutamate = D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) greater than homocysteate greater than quisqualate greater than aspartate greater than ibotenate. N-acetyl-aspartyl-glutamate was without effect. In addition, in the range of concentrations of 10(-6) to 10(-3) M, the maximal response of glutamate was higher than that of kainate, AMPA or homocysteate, whereas the effects of quisqualate, aspartate and ibotenate, particularly, were of lower amplitude. In favor of the existence of glutamate receptors of the AMPA type on dopaminergic nerve terminals, the stimulatory effect of AMPA (5 x 10(-5) M) on [3H]dopamine release was antagonized by 6,7-dinitroquinoxaline-2,3-dione, 6-cyano-7-nitro-quinoxaline-2,3-dione, tau-D-glutamyl-amino-methyl-sulphonate and tau-D-glutamyl-glycine tested at 10(-4) M. 6,7-Dinitroquinoxaline-2,3-dione was the most potent, whereas L-glutamate diethylester was without effect. As expected D-2-amino-5-phosphonovalerate did not affect the AMPA-evoked response. Further experiments indicated that kainate and quisqualate stimulate the release of [3H]dopamine by acting on quisqualate/kainate or AMPA receptors. The quisqualate-evoked desensitization of AMPA receptors was prevented by concanavalin A (10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Respective contributions of neuronal activity and presynaptic mechanisms in the control of the in vivo release of dopamine.

Studies performed in several in vivo and in vitro conditions have demonstrated that the release of dopamine from nerve terminals of the nigrostriatal dopaminergic neurons depends not only on the activity of dopaminergic cells but also on presynaptic regulations by heterologous fibers. The presynaptic facilitation of dopamine release by the cortico-striatal glutamatergic neurons has been particularly investigated. A quisqualate/kainate receptor subtype is involved in the direct (tetrodotoxine-resistant) presynaptic regulation of dopamine release by glutamate. The respective roles of presynaptic events and nerve activity in the control of dopaminergic transmission are discussed.

Animals↗
PubMed1988

Substance P and neurokinin A regulate by different mechanisms dopamine release from dendrites and nerve terminals of the nigrostriatal dopaminergic neurons.

Numerous striatal neurons innervating the substantia nigra contain substance P and/or neurokinin A. In contrast to substance P or neurokinin A, little neurokinin B is found in the substantia nigra. This led us to compare the effects of nigral application of these tachykinins on the release of dopamine from dendrites and nerve terminals of nigrostriatal dopaminergic neurons. Experiments were made in halothane-anesthetized cats implanted with one push-pull cannula in the substantia nigra and another in the ipsilateral caudate nucleus [3H]Tyrosine was delivered continuously to each push-pull cannula and the release of newly synthesized [3H]dopamine measured in the superfusate. Unlike substance P or neurokinin A, neurokinin B (10(-8) M) applied for 30 min into the pars compacta of the substantia nigra was without effect on the release of [3H]dopamine from nerve terminals or dendrites. When either substance P (10(-8) M) or neurokinin A (10(-8) M) was applied into the pars compacta, the release of [3H]dopamine from nerve terminals was enhanced. While neurokinin A also stimulated the dendritic release of [3H]dopamine, this was reduced by substance P. At a lower concentration (10(-9) M), neurokinin A induced similar effects to those observed at 10(-8) M whereas substance P (10(-9) M) stimulated moderately [3H]dopamine release from nerve terminals but did not affect the dendritic release of the [3H]amine. When superfused into the pars reticulata, substance P (10(-8) M) still stimulated [3H]dopamine release from nerve terminals but not from dendrites while neurokinin A (10(-8) M) was without effect either in the caudate nucleus or the substantia nigra. Additional experiments were made to determine whether or not substance P (10(-8) M) or neurokinin A (10(-8) M) act directly on nigral dopaminergic neurons when applied into the pars compacta. The effects of substance P on [3H]dopamine release from nerve terminals and dendrites were prevented when 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M), an antagonist of glutamatergic transmission, was applied continuously into the caudate nucleus. In contrast, the stimulatory effects of neurokinin A on [3H]dopamine release from nerve terminals and dendrites were insensitive to 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M). These results suggest that neurokinin A, but not substance P, acts directly on dopaminergic cells. In the light of previous observations, we propose that the effects of substance P on dopaminergic transmission are mediated by a nigro-thalamo-cortico-striatal loop.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Effects of kelatorphan and other peptidase inhibitors on the in vitro and in vivo release of methionine-enkephalin-like material from the rat spinal cord.

The effects of the novel mixed peptidase inhibitor, kelatorphan [N-(R)-3-(N-hydroxyaminocarbonyl-2-benzyl-1-oxopropyl)-L-alanine], were compared to those of a combination of the potent "enkephalinase" inhibitor thiorphan and the nonselective aminopeptidase inhibitor bestatin, on the catabolism of [3H]Met-enkephalin and on the release of endogenous Met-enkephalin by the rat spinal cord in vitro and in vivo. At 20 microM, kelatorphan almost prevented completely the degradation of exogenous [3H] Met-enkephalin by slices of the dorsal zone of the lumbar enlargement. Similarly, the addition of 20 microM kelatorphan to a [3H] Met-enkephalin-containing artificial cerebrospinal fluid superfusing the whole spinal cord of halothane-anesthetized rats efficiently protected the exogenous peptide from enzymatic degradation. In contrast, in the same in vitro and in vivo models, thiorphan (1 microM) or bestatin (20 microM) alone was inactive, and only their combination induced a significant protection of the exogenous peptide. In vitro and in vivo, kelatorphan (20 microM) increased markedly the spontaneous outflow of endogenous Met-enkephalin-like material as well as the peptide overflow due to K+-induced depolarization (in vitro and in vivo) or noxious stimulation (in vivo). Under similar conditions, thiorphan (1 microM) plus bestatin (20 microM) also enhanced the efflux of Met-enkephalin-like material, but generally to a lower extent than kelatorphan. Compared to thiorphan plus bestatin, kelatorphan exerts additional inhibitory effects on dipeptidylaminopeptidase activity and the present results could indicate that this enzyme also may be involved in the inactivation of extracellular Met-enkephalin at the spinal level in rats.

Animals↗
PubMed1985

Local and remote effects of intra-caudate administration of GABA-related drugs on Met-enkephalin release in the basal ganglia.

The possible influence of GABAergic systems on the activity of enkephalinergic neurones within the basal ganglia was examined by measuring the release of Met-enkephalin in the caudate nuclei and pallida of halothane-anesthesized cats treated by intra-caudate applications of GABA-related drugs. Depending on the concentration used, GABA exerted local stimulatory (at 10 microM of the amino acid) or inhibitory (at 0.5 mM) action on Met-enkephalin release in the cat caudate nucleus. Only the inhibition was reproduced by the GABA agonists muscimol (1 microM) and (-)-balcofen(10 microM) and by diazepam 10 microM). Conversely, the intra-caudate application of the GABA antagonist bicuculline enhanced markedly the local release of the pentapeptide. Complementary studies using slices of the rat striatum (caudate nucleus + putamen) revealed that a low concentration of GABA (10 microM) tended to increase the K+-evoked efflux of Met-enkephalin, whereas a high concentration of the amino acid exerted a strong inhibitory effect on the peptide release. Such in vivo and in vitro findings suggest that the GABA-induced inhibition of Met-enkephalin release took place via the stimulation of specific GABA A and GABA B receptors within the caudate nucleus, whereas the GABA-induced increase of the peptide release might involve some intracellular regulatory processes in striatal neurones containing both GABA and enkephalins. In addition to altering the local release of Met-enkephalin, intra-caudate applications of GABA-related drugs affected the peptide release in the ipsilateral globus pallidus and contralateral basal ganglia. The observed changes suggest that GABA A, but not GABA B, receptors participated in some tonic inhibitory influence of striatal GABAergic neurones on the striato-pallidal enkephalinergic system. Furthermore, the present results confirmed previous studies (Bourgoin et al.) showing that GABAergic neurones can contribute to some bilateral modulation of enkephalinergic neurones within the basal ganglia.

Animals↗
PubMed1985

Spontaneous and evoked release of methionine-enkephalin-like material from the rat spinal cord in vivo.

In vivo perfusion of the subarachnoid space with an artificial cerebrospinal fluid (CSF) in paralyzed halothane-anesthetized rats allowed the collection of methionine-enkephalin (Met-Enk)-like material (MELM) released from the spinal cord. Bio-Gel P2 chromatography and high-performance liquid chromatography showed that 65% of this material corresponded to authentic Met-Enk. Under resting conditions, about 1 pg of MELM per minute was regularly released for at least 3 h; for Met-Enk, this value corresponded to a fractional rate constant of 0.002% (i.e. tissue content of the pentapeptide which was released per minute from the whole spinal cord). Perfusion with K+-enriched (40-60 mM) CSF resulted in a marked enhancement (+ 150-200%) of spinal MELM release. Similarly, calibrated pinches of the muzzle and i.p. administration of acetic acid, two strong noxious stimuli in awake animals, induced a significant increase (+ 75-150%) in spinal MELM release. In contrast, pinches applied to the tail did not enhance but instead slightly reduced (-35%) MELM release from the rat spinal cord. These data suggest that mechanisms other than segmental controls could be involved in the activation of spinal enkephalinergic neurons by some nociceptive stimuli.

Animals↗
PubMed1985

[The spinal enkephalinergic and serotoninergic systems in the control of transmission of nociceptive messages].

Numerous anatomical, pharmacological and electrophysiological data described in the literature indicate that spinal enkephalinergic and serotoninergic systems are probably involved in the control of nociceptive inputs from the periphery to the cerebral cortex. However, reported evidence was generally indirect and did not provide a real demonstration of the physiological participation of these neurones in pain control. This led us to select appropriate experimental approaches for studying directly the activity of spinal enkephalinergic and serotoninergic systems in animals (rat, cat) submitted to noxious stimuli. Owing to two catheters introduced into the subarachnoidal space of anesthetized rats, it was possible to perfuse the whole spinal cord with an artificial cerebro-spinal fluid and thus collect the neuroactive compounds released by spinal neurones (at least those in superficial layers) under various experimental conditions. Using this technique, we observed that some (but not all) nociceptive stimuli such as intense pinching of the muzzle, intraperitoneal injection of acetic acid or noxious heat applied to the muzzle or the tail induced a significant increase in met-enkephalin release from the spinal cord (see fig. 2). Similar effects were observed following the blockade of enkephalin catabolism by thiorphan and bestatin (see fig. 1) indicating that they were not due to some alteration of peptidase activities but really involved the activation of spinal enkephalinergic systems. Since cervical cord transection suppressed the stimulatory action of noxious stimuli on spinal met-enkephalin release, it could be proposed that the mechanisms involved were not limited to the cord but depended on supraspinal structures. Bulbo-mesencephalic serotoninergic neurones projecting to the spinal cord might well correspond to such structures (or at least to some of them) since nociceptive stimuli (such as noxious heat applied to the tail) also evoked a marked increase of serotonin (5-HT) release at the spinal level (fig. 3). Such observations together with indirect evidence reported in the literature suggested therefore that the activation of spinal enkephalinergic systems triggered by noxious stimuli might result from excitatory influence due to descending serotoninergic projections. However, in vitro studies using slices of the dorsal zone of the rat lumbar cord did not reveal any stimulatory effect of 5-HT on the spontaneous or K+-evoked release of met-enkephalin (fig. 4).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Biochemical evidence for the 5-HT agonist properties of PAT (8-hydroxy-2-(di-n-propylamino)tetralin) in the rat brain.

In vitro investigations revealed that PAT (8-hydroxy-2-(n-dipropylamino)tetralin) interacted with postsynaptic 5-HT receptors in the rat brain: the drug stimulated 5-HT-sensitive adenylate cyclase in homogenates of colliculi from new-born rats (KAapp 8.6 microM) and inhibited the specific binding of [3H]5-HT to 5-HT1 sites. The PAT-induced inhibition of [3H]5-HT binding showed marked regional differences compatible with a preferential interaction of PAT (IC50 2 nM) with the 5-HT1A subclass. As previously seen with 5-HT agonists, the efficacy of PAT for displacing [3H]5-HT bound to hippocampal membranes was markedly increased by Mn2+ (1 mM) and reduced by GTP (0.1 mM). PAT also affected presynaptic 5-HT metabolism since it inhibited competitively (Ki 1.4 microM) [3H]5-HT uptake into cortical synaptosomes and reduced (in the presence of the 5-HT uptake inhibitor fluoxetine) the K+-evoked release of [3H]5-HT previously taken up or newly synthesized from [3H]tryptophan in cortical or striatal slices. This latter effect was prevented by 5-HT antagonists (methiothepin, metergoline) suggesting that it was mediated by the stimulation of presynaptic 5-HT autoreceptors by PAT. Like 5-HT, PAT counteracted the stimulatory effect of K+-induced depolarization on the synthesis of [3H]5-HT from [3H]tryptophan in cortical slices. It is concluded that PAT is a potent 5-HT agonist acting on both post- and presynaptic 5-HT receptors in the rat brain.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1984

Normal CSF levels of met-enkephalin-like material in a case of naloxone-reversible congenital insensitivity to pain.

In a case of naloxone-reversible congenital insensitivity to pain, met-enkephalin-like immunoreactivity in the CSF was in the normal range and not affected by the administration of naloxone. Chromatographic analysis of the met-enkephalin-like material revealed that it corresponded to at least two classes of molecules. A clear difference in the relative proportions of these two classes was detected in the CSF of the patient insensitive to pain when compared to controls. The possible functional significance of this alteration is discussed in relation to the well known antinociceptive action of enkephalins.

Adult↗